Chemical vapour deposition is a well-known method for depositing films or coatings on substrates. One known chemical vapour used for depositing a nickel film or coating on a substrate is nickel carbonyl in the so-called Nickel Vapour Deposition process (NVD). Typically, the substrates to be nickel coated are heated within a reaction or deposition chamber to a predetermined suitable reaction temperature, typically 110.degree. C.-180.degree. C. in an atmosphere of nickel carbonyl, Ni(CO).sub.4. The nickel carbonyl reacts at the surface of the heated substrate to deposit the Ni film or coating thereon.
Nickel carbonyl from a liquid supply tank flows through a vapourizer where it is converted into a gas stream to which gaseous stream may be added a small amount of carrier gas, such as carbon monoxide.
Typically, nickel carbonyl vapour is continuously introduced to the deposition chamber, wherein it reacts to produce elemental nickel and carbon monoxide by-product. The spent gas is continuously purged from the chamber in order to maintain proper circulation of reactive nickel carbonyl across the surfaces of the substrates. The substrates may be heated according to well-known methods, such as heat conduction, radiation, inductance and the like.
The spent gases which contain nickel carbonyl in excess of 30% W/W generally undergo a nickel carbonyl reclamation process to substantially remove the nickel carbonyl before the spent stream enters an incinerator. The incinerator is used to ensure complete thermal destruction of nickel carbonyl prior to letting the combustion products into the environment.
The recovered nickel carbonyl is, typically, passed to a liquid supply tank. Nickel carbonyl is produced in a nickel carbonyl generator containing nickel powder of a suitable morphology in a packed bed through which is passed fresh carbon monoxide gas from a storage cylinder to generate fresh nickel carbonyl. The gaseous mixture is passed through a condenser wherein the nickel carbonyl is condensed and fed to a storage tank. A compressor recirculates the resultant gas back to the nickel carbonyl generator.
The above general process represents a typical operation involving, in effect two distinctive processes for generating, reacting and re-generating nickel carbonyl with non-recycled carbon monoxide.
The above process, thus suffers from the disadvantages of wasting carbon monoxide generated as a by-product by the burning thereof in an incinerator and, also, the need to have the incinerator continuously operating in a continuous NVD process. Moreover, nickel oxide is produced in the incinerator during nickel carbonyl combustion.
U.S. Pat. No. 5,766,683, issued Jun. 16, 1998, to New American TEC describes a reclaim system for cooling the gases received from the plating system and cooling them to a temperature just above the freezing point of nickel carbonyl to condense out and recover the liquid carbonyl. The reclaim system includes a reclaim condenser and a vapor recovery gas receiver for receiving vapors from the reclaim system. The vapor recovery system includes a first stage compressor operatively connected to a first stage receiver for pressurizing the vapor to about 25 PSIG, and a first stage condenser operatively connected to the first stage compressor for cooling the vapors. A conduit communicates the vapor recovery system to the reactor system for forwarding the cooled vapors to a recycle pump receiver in the reactor system. A further compressor is provided in the reactor system for compressing the gases from the recycle pump receiver to about 65 PSIG. This system recovers and recycles substantial amounts of the nickel carbonyl and wherein the requirements for carbon monoxide are substantially reduced. However, U.S. Pat. No. 5,766,683 does not satisfactorily address the full recovery of nickel carbonyl for recycle within the system.
There is, therefore, a need for an improved NVD process which is more economic, safe and reliable.